The present invention relates to a vehicle idling stop system which automatically turns off and restarts an engine.
A vehicle disclosed in JP-A-H9-72266 published by the Japanese Patent Office in 1997 automatically turns off an engine in order to improve fuel efficiency when engine shutdown conditions are satisfied. Thereafter when an engine restart condition is satisfied, the engine is driven by a motor and automatically restarted.
When the vehicle is provided with a torque converter, creep torque when the vehicle starts is generated according to the input rotation speed to the torque converter. That is to say, it is generated according to the rotation speed of the engine and motor. Thus when engine restart conditions are satisfied and the vehicle starts moving, the generation of creep torque is delayed corresponding to the delay of increase of the motor rotation speed.
Normally this delay is short and it does not affect start-up performance. However deterioration in the battery or motor or increases in friction in the engine or drive system (hereafter referred to as xe2x80x9cdeterioration statexe2x80x9d) may result in weakening of the increase rate of the motor and engine rotation speed when the vehicle starts. As a result, the generation of creep torque is delayed and start-up performance reduced.
Thus it is preferable to determine whether the vehicle is in the deterioration state and to prohibit automatic shutdown of the engine (idling stop) if it is determined that the vehicle is in the deterioration state. If idling stop is prohibited, the engine will keep running even when the vehicle stops and creep torque is always generated to some extent. As a result, delay in the generation of creep torque can be prevented.
However, when the vehicle is on an up-slope, the increase rate of the rotation speed of the motor and engine will weaken due to increases in resistance applied to the drive wheels even when the vehicle is not in the deterioration state. Thus when the determination deterioration state is performed, it is necessary to distinguish the up-slope situation from the deterioration state.
Furthermore when the vehicle is restarted on an up-slope, the vehicle start-up performance is reduced if start-up control for a flat road is performed, because sufficient driving torque for the resistance applied to the drive wheels is not obtained.
It is therefore an object of this invention to provide a vehicle idling stop system which accurately detects deterioration state. It is a further object of this invention to allow smooth restarting of the vehicle even when the vehicle is on an up-slope.
In order to achieve above object, this invention provides a vehicle idling stop system comprising an engine, a motor which is connected to the engine, a torque converter, a drive wheel which is connected to either of the engine and the motor via the torque converter and which is driven by either of the engine and the motor, and a microprocessor. The microprocessor is programmed to determine whether an engine shutdown condition is satisfied when the engine is running, shut down the engine when the engine shutdown condition is satisfied, determine whether engine restart condition is satisfied when the engine is shut down, drive the engine with the motor and determine whether the vehicle is on an up-slope when the engine restart condition is satisfied, determine whether an increase rate in the rotation speed of the engine before restarting the engine after start up of driving of the engine with the motor is lower than a predetermined rate when the vehicle is not on an-up slope, and prohibit the shutdown of the engine based on the engine shutdown condition when it is determined that the increase rate in the rotation speed of the engine is lower than the predetermined rate.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.